Solvent extraction of waxy oils



March 7, 1939. A. B. BROWN 2,149,574

SOLVENT EXTRACTION OF WAXY OILS Filed June 29, 1956 Waxy chal'qinq'sfockf Rafflhare 23 f0 solvenf recovery Exfra cf )0 .so/vem recoverx ChlorexINVENTOR Hr ynBJiro n ATTORNEY Patented Mar. 7, 1939 PATENT OFFICESOLVENT EXTRACTION OF WAXY OILS Arthur B. Brown, Hammond, Ind., assignorto Standard Oil Company, Chicago, 111., a corporation of IndianaApplication June 29,

8 Claims.

This invention relates to improved methods and systems for the solventextraction of waxy oil stocks and it pertains more particularly to therefining of wax bearing petroleum oils for the separation of parafllnicfrom naphthenic components by means of solvents such as dichlorethylether which operate at temperatures between about 50 and 125 F.Dichlorethyl ether is commonly known in the art as Chlorex and 10 willhereinafter be referred to as such.

The most desirable operating temperatures for solvent, extractionsystems are those which do not require excessive amounts of heating orrefrigeration or, in other words, are temperatures 5 of about 50 to 125F. Many of the most effective and most satisfactory solvents, such asChlorex, aqueous phenol and cresylic acid, chlorophenol mixtures, nitrobenzene, etc. operate in this general temperature range. It has been 59found, however, that when the lubricating oil stocks contain appreciableamounts of wax, particularly crystalline wax, the undewaxed stock isdifficult to handle in this temperature range because the solidificationof the wax results in a soupy mixture or buttery mass which is extremelyhard to handle in ordinary mixers and settlers and which it ispractically impossible to separate from solvent extract mixtures withoutthe use of centrifuges.

The object of my invention is to provide methods and means for solventextracting such wax bearing oils inordinary settlers or countercurrenttowers.

A furtherobject of my invention is to increase the yield of paraflinicoils obtainable from any given stock or, in other words, to prevent theloss of paraflinic oils with extract material. A further object is toprovide a system for solvent extracting waxy-oils in a packedcountercurrent tower by means of solvents such as Chlorex andchlorophenol without encountering difilculties due to solidification ofwax and entrainment of solvent extract material by said wax. Otherobjects will be apparent as the detailed description of my inventionproceeds.

In practicing my invention I employ a countercurrent system which maybe'either a and I introduce the waxy oil stock at an intermediate pointin the system and I maintain the temperature at this intermediate pointhigher than the temperatures on both sides of this point. For instance,in a packed countercurrent Chlorex tower I introduce waxy oil at atemperature of 66 about 125 F. at an intermediate and preferably packedtower or a multiple batch countercurrent system I 1936, Serial No.87,917

relatively high point in the tower (above the packed portion). TheChlorex is introduced at the top of the tower and the temperaturegradient in the upper part of the tower may be gradually decreasedtoward the raffinate exit point due to 6 heat losses due to radiationand due to the lower temperature of the incoming Chlorex. Practicallyall of the wax remains in the upper part of the tower and it thereforedoes not clog the packing material in the lower part of the towerwherein it is essential that good contact be maintained betweenliberated or undissolved paraffinic oils and solvent. I maintain theextract exit at a relatively low temperature, preferably about 50 F.,since I have discovered that it is the extract 5 exit temperature which,in effect, prevents the loss of paraffinic oils from the system andtherefore insures maximum yields of high quality lubricating oils.

The invention will be more clearly understood 20 by reference to theaccompanying drawing wherein similar parts are designated by likereference characters in the two figures and wherein:

Figure 1 is a diagrammatic elevational plan of a multibatchcountercurrent extraction system; 5 and Figure 2 is a vertical sectionof a packed countercurrent extraction tower diagrammaticallyillustrating the invention.

Any solvent may be used in practicing my in- 80 vention which has anoperating range within about 0 to 150 F. or preferably within about 50to 125 F. Preferred examples are Chlorex, ortho monochlorophenol andchlorophenol mixtures, aqueous chlorophenol, aqueous phenol, 85 aqueouscresylic acid or aqueous phenol-cresylic acid mixtures, nitro-b'enzol,etc. The invention will be described in connection with Chlorex systems.The oil to be treated may be a distillate or residual stock which may ormay not have an undergone previous treatments to remove asphalts, resinsor other undesirable materials. For instance, the stock may haveundergone precipitation with propane for removal of asphalts and resins,it may have been subjected to a light acid treatment or, particularly inthe case of extremely naphthenic oils, it mayhave undergone apreliminary solvent extraction treatment to remove extremely low gradematerials. In the preferred example I will describe the extraction of aMidcontinent distillate stock having a viscosity of about seconds at 210F., but it should be understood that the invention is equally applicableto other distillates, other crudes and other conditions.

Referring to Figure 1, a multistage extraction system is indicated asstages A, B, C, D and E, beginning with the stage of extract removal,although it should be understood that any number of stages may be used.Chlorex is introduced through line I and admixed with raflinate materialfrom stage D from line H in mixer H, the mixture being introduced at themiddle of settler 63 in stage E. The final raflinate from this stage isremoved through line H. An extract material from stage E is returnedthrough line I and admixed with raiiinate material from stage C fromline I 6 in mixer I I, this mixture being introduced at the center ofsettler la in stage D. Extract material from this stage is returnedthrough line 19 for admixture with raihnate material from stage B whichis introduced through line 22 and 'heater 23, the temperature of theheater being suflicient to maintain the temperature of the entiremixture in the following stage at about 125 F. The solvent extractmaterial from line H! is intimately mixed with raflinate material fromline 20 and incoming stock from line 22 in mixer 2| and'this mixture isintroduced into the middle of settler 24 in stage C.

Extract from this settler is withdrawn through line 25 and mixed withraffinate material from stage A which is introduced through line 26 intomixer 21, the mixture being introduced into the middle of settler 28 ofstage B.

The extract material from stage B, which is preferably maintained at atemperature of about 100 F., is withdrawn through line 29, exchanger 30and cooler 30a. and introduced at the center of settler 3| in stage A,final extract material being withdrawn through line 32 to the extractsolvent recovery system.

It will be noted that the extract entering stage A is not mixed with anyother material but is merely cooled to a low temperature to effect theseparation in this stage which is preferably maintained at about F. orlower. I have found that the temperature of the extract exit stagedetermines the selectivity of the extraction. The temperature at therafilnate end of the system may be considerably higher but there will beno loss of selectivity in the system as a whole if the temperature atthe extract end of the system is maintained sufficiently low (provided,of course, that adequate means are provided for the separation ofparaiiinic oil from solvent in this low temperature zone). Otherconditions being equal, the lower the temperature of extraction at theextract end, the better will be the selectivity.

It will be noted that the wax will be concentrated in my improved systemin stages C, D and E which are all operating at relatively hightemperatures. The wax which meets incoming solvent in stage E issubstantially freed from asphaltic and naphthenic materials andtherefore causes no entrainment or separation problems. If this wax werepresent in stages A and B there would be mechanical entrainment ofphases between stages with resulting lowering of effectiveness of thestage compared with the theoretical stage.

As indicated in the drawing, a preferred range of operating temperaturesis 50, 112 and 100, respectively, for stages A, B, C, D and E. It shouldbe understood, however, that these temperatures are merely illustrative;that temperatures as high as may be used in stage C; that thetemperature in stages C, D and E may be substantially constant; and thattemperatures as high as 75 or as low as 0 F. may be used in stage A. Inthe case of low miscibility temperatures solvents such as nitro benzenerefrigeration need be applied only to the extract exit end ofthe system.Suitable heat exchange may be employed throughout the various parts ofthe system as will be apparent to those skilled in the art.

My invention is of still greater significance in I systems employingpacked countercurrent extraction towers since it is practicallyimpossible to countercurrently extract a soupy wax slurry inconventional equipment. In accordance with my invention the incomingstock through line 22 is passed through heater 23 so that the waxoilsolution will be mobile and fluid and at a temperature of about 120 to150 F. This mixture is introduced into countercurrent tower 33 above thepacked portion thereof. Under conditions at this point in the towerthere will be a substantially complete separation of the wax fromnaphthenic materials, the wax being carried upwardly with the rafiinateand the naphthenic' materials with entrained naphthenic 011 beingcarried downwardly through the packed section of the tower.

Chlorex or other solvent may be introduced at.

the top of the tower through line l0 and rafllnate may be removedthrough line H, the top of the tower being maintained at a temperatureof about 100 F.

The packing material 34 in the lower part of the tower may be of anyconventional type of material such as graphite, Raschig rings, glassbeads, porcelain figures, steel jack chain or steel turnings. I havefound that the steel tumings or steel springs giveexcellent contact inthis portion of the system but I donot limit myself to any particulartype of packing material.

The temperature gradient in the lower part of the tower is graduallydecreased from the point of charging stock introduction to the extractremoval through line 32. This lowering of temperature is preferablyeffected by a series of pancake coils 35, 36, 31 and 38 so that at thebottom. of the tower the temperature is about 50 al-- though it may beas high as '75 and as low as 0 F.

As the mixture is cooled in-the lower part of this packed towerparafflnic oils are released from the solvent extract solution and therelease of such oils is materially facilitated and expedited by the useof the packing material. Ordinarily it is unnecessary to introduce anystripping or washing fluid at the base of the acid, chlorophenol, etc.

In the above example the proportions of solvent to oil are usually abouttwo to one, although these proportions may vary from one to one-to threeto one and the exact diluent ratio must be determined in every case bythe nature of available stock and the specifications of the desiredproduct.

By operating all but the extract stages at high temperature I effect aconsiderable saving in refrigeration and by eliminating the wax fromployed I increase the eflectiveness and efliciency of refrigeration. Thesaving in refrigeration, together with the increased selectivity ofextraction and the increased ease of separating raffinate from extractmaterial makes my improved process one of great commercial importance inthe refining of wax bearing lubricating oil stocks.

, oil is fluid and mobile, introducing solvent at the top of said towerand flowing downwardly in said tower countercurrent to the upward flowof paramnic and waxy materials, withdrawing extract irom the base ofsaid towerand cooling the extract material in the lower part of thetower whereby the parafllnic oil is released from the extract solutionand the downcoming extract solutionis contacted with said releasedparafilnic oil in the packed section of the tower.

2. The'method of claim 1 wherein the tem:- perature in the base of thetower is from 0 to F.

3. The method of claim I wherein dichlorethyl ether is the extractingsolvent and the ggmperature at the base of the tower is about 4. Themethod of claim 1 which also includes the introduction at the base ofthe tower of a light stripping liquid for facilitating the removal ofparafiinic oil from extract material in the packed section of the tower.

5. The method of claim 1 wherein propane is introduced in the lower partof the tower.

6. The method of countercurrentiy extracting a waxy oil stock in apacked tower which comprises introducing said stock at a pointin thetower above the packing material and at a temperature of at least F.,introducing solvent at the top 01 said' tower and countercurrcntlycontacting said stock with said solvent in the upper part of said towerat a temperature at which the wax is in liquid phase, efiecting aseparation of parafllnic oil from the extract in the lower part of saidtower and contacting said separated oil with downcoming extract in thepacked section or the tower.

'7. The method of claim 6 wherein the separation in the lower part ofthe tower is effected by chilling to a temperature not higher than 50 F.

8. The method oi claim 6 wherein the separation in the lower part of thetower is efiected by a modification oi the solvent caused by theintroduction of a liquid to bring about a separation of parafllnic oilfrom extract.

ARTHUR B. BROWN.

